THEORY VERSUS EXPERIMENTS IN TWO-DIMENSIONAL SURF BEAT

Hemming A. Schaffert, Ivar G. Jonsson

Abstract

Comparison is made between a deterministic infragravity-wave model and existing laboratory experiments. The theoretical model considers incident bichromatic waves including the effects of the accompanying incident long, bound wave, an oscillating position of the break point, and the intrusion of short-wave grouping into the surf zone, whereas frictional effects are neglected. A measure of the infragravity wave activity is the amplitude of a seaward progressing free, long wave. For this amplitude the qualitative agreement between theoretical results and experiments is excellent. Quantitatively the theory overestimates the infragravity waves by typically 50-100%. This may in part be attributed to the neglect of frictional effects.